A tokamak reactor is a known type of thermonuclear fusion reactor, involving a generally doughnut-shaped vessel or casing, in which a vacuum is maintained. A thermonuclear reaction is produced in a high temperature plasma, circulating within the vessel. The plasma produces a high heat flux and also a high neutron flux. The heat flux is transferred to and removed by a coolant, such as high pressure helium, circulated through passages which are separated from the vacuum space by the first wall of the reactor. Such passages may also contain lithium in some form, such as lithium oxide, which is bombarded by the neutron flux to produce tritium, for use as thermonuclear fuel.
Thus, the first wall is subjected to an extremely high heat flux and a high neutron flux on one side, while being subjected to a high pressure on the opposite side. The first wall must be able to withstand the high heat flux, the high neutron flux and the high pressure.
In various known tokamak reactor constructions, the first wall includes a plurality of hollow lobes, in which the lithium oxide or the like is present, and through which the helium coolant is circulated. Tubular members may be provided within the lobes, to contain the lithium or lithium oxide. Each lobe comprises a pair of side wall portions and a curved end wall portion extending therebetween. In the known constructions, the curved end wall has a substantially cylindrical curvature.
The pressurized helium coolant, within each lobe, exerts a high fluid pressure on the concave side of the curved end wall. Due to the substantially cylindrical curvature of the end wall, the pressure produces substantially pure tensile stresses in the curved end wall. Thus, the curved end wall is loaded in substantially pure membrane tension by the pressurized coolant.
The convex side of the curved end wall confronts the extremely hot plasma, which produces a high heat flux and a high neutron flux, directed upon the convex side. Due to the coolant on the concave side and the high heat and neutron fluxes on the convex side, there is a large temperature differential between the convex side and the concave side of the curved end wall. If the end wall were flat and unrestrained, it would tend to warp into a spherically curved shape, due to the high temperature differential between the hot and cool sides of the wall. However, the cylindrically curved end wall is restrained against such warpage, with the result that high thermal stresses tend to develop in the curved end wall, due to the high temperature differential between the convex and concave sides of the wall. The high thermal stresses limit the practicality of this design.
The present invention is directed to the problem of dealing more effectively with this difficult combination of pressure stresses and thermal stresses in the first wall.